The use of various types of biologically active cells as components of implanted devices for the purpose of delivering bioactive agents produced by said cells is well known in the art. Various attempts to devise methods for enhancing the survivability of such implanted cells have ultimately fallen short and require either the vascularization of the implant or a maximum diffusion distance of about 2-3 mm in order to provide nutrients to the cells. These various types of cells include fibroblasts, myoblasts, stem cells, progenitor cells, mature differentiated tissue cells, and undifferentiated cells.
Chondrocytes offer several unique advantages as vehicles for expressing therapeutic agents over other cell types. For example, chondrocytes do not require vascular support, and therefore can readily be used in environments that have a reduced, or non-existent vascularization system. Furthermore, chondrocytes are able to survive in harsh in vivo environments, including low pH and low oxygen surroundings. In addition, there is a reduced likelihood of malignancy due to the anti-angiogenic properties of normal chondrocytes. Chondrocytes also possess an immune privileged property which reduces immune rejection of co-implanted allogenic or xenogenic tissue. Furthermore, chondrocytes are more easily scalable compared to other normal untransformed cell strains.
Chondrocytes are typically involved in cartilage repair. Cartilage is a structural support tissue that is found in the body in three main varieties. Hyaline, or articular cartilage, helps dissipate loads in joints. In articular cartilage, chondrocytes are encapsulated in a woven, mesh-like matrix of type II collagen and proteoglycans. Elastic cartilage provides flexible support to external structures, and is composed of chondrocytes embedded in a matrix of collagen and elastic fibers. Fibrocartilage aids in transferring loads between tendons and bone. It consists of an outer layer of collagen and fibroblasts that support and inner layer of chondrocytes that make type II collagen fibers.
To date chondrocytes have been used to correct or repair cartilaginous defects. For example, by placing chondrocytes into hydrogels and injecting the chondrocytes into a cartilage defective region. The chondrocytes are used to express matrix proteins required for cartilage repair. Although chondrocytes have been cultured and placed into substrates such as hydrogels, for treatment, or repair of cartilage or bone defects, there is no teaching in the art that chondrocytes can be used to express therapeutic agents for the treatment of pathologies or injuries other than cartilage tissue.
However, there remains a need for devices and methods capable of delivering a large volume of such genetically-altered chondrocytes to various treatment sites not typically associated with chondroctyes.